Filtering system

ABSTRACT

A filtering system comprising an inlet ( 11 ) for liquid to be filtered and an outlet ( 9 ) for filtered liquid, as well as filtering means, which system is characterized in that the filtering means, placed in series comprise: a first filter ( 2 ) comprising activated carbon with the capability to also remove particles that are larger than approximately 0.5 μm; an ultrafiltration membrane ( 5 ) for the removal of particles that are larger than approximately 0.02 μm; a post-treatment filter ( 14 ) of activated carbon, optionally provided with a microfiltration membrane ( 13 ), wherein the system also comprises a vessel ( 6 ) for filtered water located between the ultrafiltration membrane ( 5 ) and the post-treatment filter ( 14 ), with the option of using the filtered water from the vessel for back-flushing the ultrafiltration membrane ( 5 ).

[0001] The present invention relates to a filtering system, inaccordance with the preamble of claim 1. The invention also relates to amethod of cleaning an ultrafiltration membrane module, which is part ofthe filtering system according to the invention.

[0002] A filtering system as mentioned in the preamble of claim 1 isknown from Patent Abstracts of Japan, Vol. 2000, no. 2, 29 Feb. 2000 andJP 11.319827 A, Said known filtering system yields drinking watercontaining minerals and prevents backgrowth of bacteria from the outlet.

[0003] However, said known filtering system has a disadvantage in thatthe use of a nanofiltration membrane only provides a low flow ratethrough the filter. Therefore, much of the feed water is wasted in thisprocess. Also, the water becomes stagnant in the module. Since inlinecleaning is technically not possible in said known filtering system,bacteria and viruses may accumulate in the module, multiply andeventually pass teak spots in the membrane and the module connectors andcontaminate the vessel for storage of filtered water.

[0004] The object of the present invention is to provide an improvedsystem in which the above-mentioned drawbacks are eliminated. It is aparticular object of the invention to provide a system in which drinkingwater may be produced without losing a great deal of water.

[0005] The present invention provides the advantage that the use of anultrafiltration membrane makes a larger flow rate through the filterpossible. Furthermore, so as to provide for a cleaning of saidultrafiltration membrane, the valve, which is provided between the firstfilter and the ultrafiltration membrane makes it possible that theultrafiltration membrane is backwashed. Filtered water which is storedin the vessel flows back through the ultrafiltration membranes andremoves any contamination which has been held back by theultrafiltration membrane, after which said contaminants, together withthe water, may be drained through the said valve and discarded.

[0006] The advantage to be obtained with the filter system of thepresent invention is that the ultrafiltration go membrane may be keptclean by backwashing said ultrafiltration membrane with sterile waterfrom the vessel. Therefore, the ultrafiltration membrane does not haveto be dismantled so as to have it cleaned.

[0007] Therefore, according to another aspect of the invention, it alsorelates to a method of cleaning the ultrafiltration membrane module,which is part of a system according to the invention, in accordance withclaim 8.

[0008] As a matter of fact, reference is made to JP 11 309447 A (PatentAbstracts of Japan, Vol. 2000, no. 2, 29 Feb. 2000) in which anultrafiltration membrane is mentioned, in the form of a hollow fibremembrane filter, capable of passing all minerals without any water loss.However, said reference does not mention a valve, which makes itpossible to clean an ultrafiltration membrane by means of backwashing.

[0009] Also, reference is made to JP 60.068093 A (Patent Abstracts ofJapan, Vol. 009, no. 200, 16 Aug. 1985), which mentions a method forfiltering water, using an ultrafiltration membrane. However, saidpublication does not mention a valve according to the present invention,with which it is possible to clean the ultrafiltration membrane by meansof backwashing.

[0010] Finally, reference is made to WO 01.07151 A (in the name of PrimeWater Systems GmbH), which describes the use of an activated carbonfilter, which is capable of removing particles that are larger then 0.5μm, as a pre-filter to an ultrafiltration hollow fibre membrane filter.However, said publication does not mention the features of the presentinvention, such as the vessel for the storage of filtered water and thevalve for making it possible to clean the ultrafiltration membrane bymeans of backwashing.

[0011] The advantage of the valve in the present invention is that thesystem can be used for filtering liquid when the valve is in the firstposition. When the valve is in the second position, filtered liquid canbe flushed back from the vessel through the ultrafiltration membrane, inorder to remove accumulated contamination from the pores. Via the valve,which is in the second position, the flushed-back filtered liquid (alsoindicated as back wash water) together with the contamination cansubsequently be discharged to the drain.

[0012] The ultrafiltration membrane and the post-treatment filter may beinterconnected by means of, for example, a tubing. In this tubing aconnection may be provided for the vessel for filtered water. Thisconnection for the vessel may consist of a branching leading from thisconnecting tubing.

[0013] As mentioned above, the ultrafiltration membrane is incorporatedin a module. This ultrafiltration module preferably consists of a bundleof hydrophilic capillary membranes having an asymmetrical pore structurewith the filtering layer on the inside of the capillary, as a result ofwhich they have a very low flow resistance, and consequently a lowpressure drop over the membranes. According to a preferred embodiment,the membranes are closed at one end and open at the other end, the spacebetween the capillary membranes and the module wall being filled withepoxy resin. The water flows through the perforated wall of the moduleand the membrane wall to the lumen of the capillaries, and is thusfiltered. Via the post-treatment filter the filtered water subsequentlyflows to the outlet or is fed to the vessel for filtered water. Such adead-end ultrafiltration module is described, for example, in theAmerican patent U.S. Pat. No. 5,895,573.

[0014] Another embodiment of the ultrafiltration module is one whereinthe membranes are open at both ends, and wherein a valve is provided atone side through which the flow passes from the inside to the outsideand wherein the filtered water exits through the side wall of themodule. Such an embodiment may be called dead-end flush. The use of sucha dead end flush module makes the above-mentioned method of cleaning theultrafiltration membrane considerably more complicated.

[0015] If the ultrafiltration membrane has a pore size of approximately0.02 μm, all the particles that are larger than this pore size will beretained. Among others, such a membrane will retain microorganisms suchas bacteria and viruses, resulting in sterilised filtered water.Compounds that are dissolved in the water, such as minerals, will passthrough the membrane. The original concentration of minerals is thusmaintained. Due to the fact that the water is continuously swirlingaround the ultrafiltration module, there will be no stagnation in themodule and the housing so that the risk of germ growth is minimised.

[0016] The first filter may be formed, for example, from a felt-likematerial in combination with activated carbon incorporated in the feltthat is formed preferably by moulding. A favourable property of such afirst filter module is that it does not, or only very slightly shedcarbon, which might clog the ultrafiltration membrane. Moreover, thisfirst filter of activated carbon provides a preliminary filtration up toapproximately 0.5 μm. A final advantage of this first filter ofactivated carbon is that the flow resistance and consequently thepressure drop over the block will be reduced compared with other typesof activated carbon filters.

[0017] In order to prevent the block of activated carbon from becomingclogged when the liquid to be filtered is more seriously contaminatedwith relatively large particles, and to prolong the life of thefiltering device, the first filter comprises according to a preferredembodiment a first filtering step provided around the block of activatedcarbon, forming a supplementary filtering step before the block ofactivated carbon.

[0018] This first filtering step may be formed, for example, from afelt-like filter, optionally folded in concertina fashion around theblock of activated carbon. These strips of such a first filtering stepthat are formed by the folds, possess a large filtering surface having avery considerable filtering capacity.

[0019] Such a filter is incorporated, for example, in a “801 seriesfilter cartridge”, available from Harmsco Industrial Filters of NorthPalm Beach, Fla., USA. A moulded block of activated carbon as mentionedabove may consist of, for example, a “C-246 series moulded block filtercartridge”, available from Fibredyne, of Dover, N.H., USA.

[0020] The back wash provision essentially consists of the valve betweenthe first filter and the ultrafiltration membrane module. When saidvalve is in the second position, water will be allowed to flow from thepressure tank via the ultrafiltration module to the drain. The sterilewater from the pressure tank (vessel for filtered water) will flow inthe opposite direction compared with the direction of flow duringfiltration, through the ultrafiltration membrane, thereby cleaning itspore structure as well as the module housing. In this way contaminantsretained by the membrane are flushed away.

[0021] The post-treatment filter is provided after the ultrafiltrationmembrane and the vessel for filtered water, but before the outlet. Thefilter consists of, for example, a cylindrical block of activatedcarbon, which may be extruded or sintered. A microfiltration module isdisposed in the central passage through the block, extending parallel tothe longitudinal axis. The water flows from the pressure tank throughthe block of activated carbon and subsequently through themicrofiltration membranes. Any harmful organic compounds possibly stillpresent in the water will be adsorbed on the activated carbon therebyallowing the taste to be further improved. The micro filtration membranemodule at the inside of the block of activated carbon provides aneffective barrier against back-growth of bacteria from the outlet intothe pressure tank. The combination of ultrafiltration before thepressure tank, micro filtration module after the pressure tank, as wellas regular washing of the ultrafiltration membrane module guaranteesthat the sterile water in the pressure tank is protected veryeffectively against bacterial contamination. In this way a very sterilesystem is provided.

[0022] The ultrafiltration membrane module may also be formed by acylindrical block, which around its circumference is provided withopenings for the inlet of water to be filtered. In this cylindricalblock the filtration membranes may be provided, analogous to the firstfilter.

[0023] Below follows a description of the figures.

[0024]FIG. 1 shows a diagram of the filtering system according to theinvention. The figure shows a housing 1 provided with an activatedcarbon first filter module 2 through which the water to be filtered isfed via an inlet 11. Such modules are known in practice. Thepre-filtered water leaves this first housing 1 and is fed via athree-way valve to the housing 4 of the ultrafiltration membrane module5. In the embodiment shown, the three-way valve 3 is in the firstposition, allowing the pre-filtered water from of the first filterhousing 1 to be fed to the second housing 4. The housing 4 comprises theultrafiltration membrane module 5. This ultrafiltration membrane module5 is cylindrical. Such an embodiment is also known in the art.Subsequently the water from the ultrafiltration membrane module is fedvia the outlet 12 to a vessel 6 for filtered water. This vessel 6 isembodied as a pressure tank. From the vessel 6 the filtered water can befed via a post-treatment filter 14 in housing 7 to a faucet 9. Thepost-treatment filter 14 is preferably comprised of a cylindrical carbonfilter having a coaxial cavity 15, in which coaxial cavity 15 amicrofiltration membrane 13 is provided. This microfiltration module ispreferably comprised of a bundle of hydrophilic membranes having anasymmetrical pore structure, with the filtering layer at the inside ofthe capillary, having a pore size of approximately 0.1 to approximately0.4 μm.

[0025] Because there is a microfiltration membrane 13 between the faucet9 and the storage vessel 6 for filtered water, no back-growth ofcontaminants via the faucet 9 to the storage vessel 6 is possible. Thisguarantees the sterility of the filtered water in the vessel 6.

[0026] When the ultrafiltration membrane 5 becomes contaminated due tothe retention of substances that have been removed from the water to befiltered, filtered water can be flushed back from the vessel 6 throughthe ultrafiltration membrane and subsequently to a drain 10. This drain10 can be reached by setting the three-way valve 3 into a secondposition as shown in FIG. 2. When flushing back, the faucet 9 must ofcourse be closed. By positioning the three-way valve 3 as near aspossible to the feed side 16 of the housing 4 of the ultrafiltrationmodule 5, and at the same time keeping the distance from the outlet 12to the vessel 6 for filtered water as short as possible, only verylittle water will be required for cleaning the ultrafiltration membranemodule 5 in accordance with the procedure described above.

[0027] The above-described sequence of separate filtering means,three-way valve and storage vessel, between the inlet and the outlet ofthe system provides a very convenient system for the purification ofdrinking water.

[0028] The invention is of course not limited to the illustrations inthe figures and the above description. A person skilled in the art willknow of further adaptations.

1. A filtering system comprising an inlet (11) for liquid to be filteredand an outlet (9) for filtered liquid, as well as filtering means(2,5,13,14), placed as modules in series, wherein the filtering means(2,5,13,14), comprise: a first filter (2) comprising activated carbonwith the capability to also remove particles that are larger thanapproximately 0.5 μm; a filtration membrane (5) for the removal ofparticles that are larger than approximately 0.02 μm; a post-treatmentfilter (7) of activated carbon (14) provided with a microfiltrationmodule (13), which is connected to the outlet (9), wherein the systemalso comprises a vessel (6) for filtered water located between thefiltration membrane (5) and the post-treatment filter (7), characterizedin that said filtration membrane (5) is an ultrafiltration membrane (5)and that a valve (3) is provided between the first filter (2) and theultrafiltration membrane (5), or is provided between the housings (1,4)in which these are accommodated, which in a first position connects thefirst filter (2) with the ultrafiltration membrane (5), and which in asecond position connects the ultrafiltration membrane (5) with a drain(10).
 2. A system according to claim 1, characterized in that each ofthe filter modules is accommodated in a separate housing (1,4,7).
 3. Asystem according to one of the preceding claims, characterized in thatthe ultrafiltration module (5) is constructed in accordance with adead-end configuration.
 4. A system according to one of the precedingclaims, characterized in that the ultrafiltration module (5) isconstructed in accordance with a dead-end flush configuration.
 5. Asystem according to one of the preceding claims, characterized in thatthe ultrafiltration module (5) comprises hydrophilic capillary membraneshaving an asymmetrical pore structure with the filtering layer on theinside of the capillary.
 6. A system according to one of the precedingclaims, characterized in that the post-treatment filter (7) comprises acylindrical block of activated carbon (14) provided with a substantiallycoaxial open cavity (15), in which open cavity (15) a microfiltrationmodule (13) is provided.
 7. A system according to claim 6, characterizedin that the microfiltration module (13) comprises hydrophilic capillarymembranes having an asymmetrical pore structure with the filtering layeron the inside of the capillary.
 8. A method of cleaning theultrafiltration membrane module (5), which is part of a system accordingto one of the claims 1 to 8, comprising the closing of the outlet (9),in counterflow conducting the filtered water from the vessel (6) inorder to remove contamination from the membrane of module (5) while thevalve (3) is in the second position, and the subsequent draining via thevalve (3) of the water and the contamination.